The purpose of this study is to determine the safety and tolerance of ascending single intravenous doses of sirolimus (rapamycin) in patients with stable renal transplants. The purpose of this study is to collect safety data on the study solution and not to formally test any statistical hypothesis. A secondary purpose of the study is to determine the pharmacokinetics of sirolimus and its effect on cyclosporine pharmacokinetics when administered concomitantly with corticosteroids.